This invention relates to the construction of a golf club and more particularly to the inclusion in a hollow golf club head of a reinforcement or secondary wall.
Golf clubs (other than the putter) are typically referred to as irons and woods. The difference (other than shaft length) is in the heads which are designed to strike a golf ball. The irons are configured as a metal (steel) blade and are used for accuracy and shorter distances as compared to woods. The heads of the woods are somewhat elliptically shaped (ellipsoid) but having a flat front striking face. Whereas woods were originally made of wood material, more recently they have been made of metal and are referred to as metal woods. This invention is directed to metal woods.
A metal wood, like its wood material predecessor, is somewhat elliptically shaped (ellipsoid). However, rather than being solid, it is hollow. An objective is to provide an appropriate balance of weight as between the shaft and the head. A further objective is to provide a desired weight distribution within the head design. A larger head requires a lighter material and vice versa. Typically the striking face is a non-soft (hard) metal to cause the ball to rebound off the face with the least amount of velocity loss. The shell of the head (extended rearwardly from the striking face) may be softer metal or simply a thinner section of the same metal to make it lighter as desired to produce weight distribution but of course maintaining a required level of structural integrity.
Within the constraints as generally described above, it is desired by the club manufacturer to produce a club head that will produce the minimum velocity loss and thus maximum distance when striking a golf ball. The present invention is directed to this objective.
The present invention provides a secondary or reinforcement wall provided in a spaced relation behind the striking face of the club head. Through experimentation it has been determined that the provision of such a secondary wall does indeed provide less loss in rebounding velocity. It has been further determined that placing the secondary wall close to the striking face but maintaining a space from the striking face, further improves the velocity loss. Manufacturing limitations dictate an optimum distance of about 6 millimeters (mm.) although distances as small as 3 mm. or even smaller are believed to produce the desired results. A spacing up to about half the distance of the club head length will produce some benefit in reduced rebounding velocity loss.
Whereas the experiments performed, involving numerous structural arrangements, have emphatically established a benefit from the use of the secondary wall, the physical properties that produce the benefits are not totally understood. The following explanation is derived from the vast array of test results but is nevertheless theoretical.
The use of a hard metal face is considered important to avoid impact absorption. Maraging Steel, a hard metal material, is considered a type of metal that is desirable as the face material. Maraging Steel is understood to have a hardness of about 47 HRC. Other acceptable metals are however available. The selection of an acceptable metal may be determined based on hardness and/or thickness such as to provide satisfactory elasticity while avoiding undesired brittleness. It also preferably has minimal plasticity which is considered to be a detrimental property of energy absorption.
Maintaining the relative properties of high elasticity/low plasticity for the striking face is an objective for achieving the desired performance. However, encasing that striking face in a thin metal shell tends to defeat this objective. The thin metal shell is considered desirable, e.g., for balancing weight. However, what is believed to happen is that the face itself transfers the impact to the shell where impact absorption occurs. The placement of the secondary wall is believed to provide a re-enforcing effect that largely restricts the transfer of the impact to the surrounding shell. The greater the distance between the two walls, the greater the undesired absorption. Retaining a short distance between the walls retains the rebounding affect of the face material. As previously indicated, a 6 mm. distance is optimum considering manufacturing limitations, e.g., for placement of the hosel and for securing the sole or ground plate and the striking face to the shell (e.g., by welding, brazing, etc.). Benefits are achieved, however, with as great as 50% of the length of the head and as close as 3 mm. or even less from the face plate.